High temperature brazing alloys

ABSTRACT

BRAZING ALLOYS COMPRISING IN PERCENT BY WEIGHT 25-70% GOLD, 5-30% PALLADIUM, 15-40% NICKEL, 4-12% CHROMIUM AND .01 TO 2% YTTRIUM. THESE ALLOYS EXHIBIT SUBSTANTIAL DUCTILITY AND HIGH OXIDATION AND CORROSION RESISTANCE AT SERVICE TEMPERATURES OF 1600-1800*F. AND ABOVE CONTINUOUSLY FOR 100 HOURS OR MORE AND THEREFORE HAVING PARTICULAR UTILITY IN JOINING STAINLESS STEEL AND SUPERALLOYS IN AIRCRAFT AND SPACE CRAFT ENGINES AND COMPONENTS. THE ADDITION OF UP TO ABOUT 2% BY WEIGHT OF TUNGSTEN, TANTALUM OR MOLYBDENUM TO THESE ALLOYS FURTHER IMPROVES THEIR HIGH TEMPERATURE STRENGTH.

Patented May 4, 1971 action of the brazing alloy with the base metal which 3 577 233 HIGH TEMPERATURI; BRAZING ALLOYS glzrreiglebieiained its original physical properties at or Nicholas T. Gamer, Palo Alto, Calif., assignor to a Western Gold & Platinum Company TABLE 1 No Drawing. Frltitlllgtat. Ser. No. 758,705 5 compositionyweight percent US. Cl. 75-134 11 Claims Chro- Molyb- Tanta- Nickel mium Yttrium denum lum ABSTRACT OF THE DISCLOSURE Brazing alloys comprising in percent by weight 2570% gold, 530% palladium, 40% nickel, 412% chromi- 31-33 6-7 201m 2... 1 28-30 8-10 .01to2 1 um and .01 to 2% yttrium. These alloys exhibit substan- A preferred method of making the brazing alloys listed tial ductility and high oxidation and corrosion resistance in Table 1 consists of melting essentially pure gold, palat service temperatures of 1600-1800 F. and above con- 15 lad and nickel in the prescribed weight ratio in a tinuously for 100 hours or more and therefore having par- Vacuum furnace and raising the temperature PP ticular utility in joining stainless steel and superalloys in mately 100 C. above the melting point of the mixture. aircraft and space craft engines and components. The Charg s of Chromium and, if required, tantalum m addition of up to about 2% by Weight of tungsten, tantalybdemlm then added, followed y the desired amount lum or molybdenum to these alloys further improves their 0f y It is important that the Yttrium element be high temperature strength. added last. Thereafter the melt is stirred and cast into an ingot which is then formed into sheet or Wire.

The addition of 0.5 %2.0% by weight of yttrium to BACKGROUND 01: THE INVENTION the melt does not necessarily mean that this element will remain in the brazing alloy in this proportion. Yttrium reacts with gases present in the melt and with the furnace atmosphere and consequently its content tends to be lower than the initial proportion. The precise amount of yttrium in the alloy is dependent on a number of factors including cleanliness of the entire system. However, the following conclusions are made from analysis of test results of alloys embodying this invention:

This invention relates to brazing alloys and more particularly to an improved alloy for joining superalloys designed for sustained service at temperatures of 1600- 1800 F. and above.

As temperature-resistant and corrosion-resistant characteristics of superalloys are improved to meet ever increasing demands of modern technology, there is an accompanying requirement for brazing alloys with sim- (1) There is diffi ulty in rolling (cold ki h ilar characteristics to join such elements. Jet englnes for alloy if the yttrium, content exceeds 5% high speed aircraft and other space vehicles, for example, (2) The addition f by Weight f yttrium to the have turb ne buckets, blades and n0zZleS Wh are p melt yields an alloy having yttrium present in a ratio of ated continuously for long periods at temperatures of 0 2 15% by i h 1 600-l800 F. and above. Under such opera g eohdi' (3) The oxidation resistance of alloys having 0.1% h h Compositions h to 10111 these engine Parts and 0.5% yttrium, respectively, is about the same. The OXIdlZe p y and l their Sifehgih- The eorroslve 40 lower limit of yttrium content for good oxidation resistproducts of combustible engine gases, such as sulfur comance was b li d t be about 0.1%, Pounds, e to penetrate the brazing h'laieflal and fllf- The alloys of Table 1 are applied to the base parts to ther contribute to the rapid deterioration of the brazed h j i d as i r strips i a onventional anner or l Such ig y Hillel also h sufficiently ductile may be formed into a flexible strip as described in Pato wi h a lh of hlghlocahzed t e ent No. 3,056,195 to facilitate proper positioning on com- An ob ect of this invent1on 1s the prov1s10n of an implexly shaped articles. Brazing preferably is accomplished proved brazing alloy which mamtains high tensile strength i a highl reducing atmosphere such as in a dry hydroand hot corrosion resistance at elevated temperatures, i.e., gen furnace or in vacuum, 1600-1800 F. for 100 hours or more. A specific example of the advantage of these improved SUMMARY OF THE INVENTION brazing alloys will now be described with respect to Al- I loy No. 2 composed essentially of 46.5% Au, 23.5% Pd, The utility of gold-palladium-mckel-chromium brazing 234% i 5% Cr and 01% A T joint was made alloys in g y corrosive oxidizing atmospheres at high with blocks of a base metal consisting of Hastelloy X temperatures is greatly improved by the addition of yttrihaving a composition in percent by weight of 22% Cr, urn. This element produces a superficial coating on the 9% M 1% Co, 185% Fe and th balan Ni, The alloy which resists Penetration of yg and nitrogen at blocks and properly positioned brazing alloy were placed high temperatures and thus preserves the strength and i a vacuum furnace at 1.5 10 mm. Hg and the temductility of joints made with the alloy. Yttrium also imperature was raised until the braze flowed at 2076 F. proves the grain refinement Within the alloy structure and Thereafter the joint was cooled. The brazed assembly prevents grain growth at high temperatures. This improves was then heated in an oxidizing atmosphere to 1800" F. the strength of the brazed joints at these elevated ternfor 400 hours. Thereafter a Knoop hardness test was peratures. conducted on a section of the joint across the fillet and DESCRIPTION OF PREFERRED EMBODIMENT base metal with the following results:

In the fabrication of high performance jet engines and TABLE 2 more particularly in the joining of stainless steel and Knoop hardness number superalloys to make hot gas turbine parts and similar as- HastelloyX Fillet semblies, brazing alloys having specific compositions given in Table 1 produced excellent bonds. These alloys exhibgit r xiiigii ci i jfjli ited good oxidation and corrosion resistance at temperatures of 1600-18'00 F. and had excellent stress rupture Metallographic examination of the fillet indicated no apcharacteristics. There was no significant intermetallic reparent oxidation penetration.

TABLE 3 Alloy Refer- 1 2 ence 4.65 5.16 37.7 None None Heavy Weight gain, mgJcmJ Flaking The reference braze not only failed this oxidation test but did so catastrophically, thereby demonstrating the high performance of the brazing alloys embodying the invention under extremely severe conditions. It is noted that the oxidation resistances of Alloy Nos. 1 and 2 are about the same but due to higher gold content, Alloy No. 2 had greater high-temperature strength and creep characteristics than Alloy No. 1.

In a test to measure corrosion resistance, T-shaped specimens of a base metal consisting of 0.1% by weight carbon, 1.5% manganese, 0.5 silicon, 20% chromium, 10% nickel, 15% tungsten, and the balance cobalt were brazed with Alloy N0. 3 and were exposed to sulfur dioxide (S with 1 ppm. salt in a furnace at 1900 F. for 16 hours. This sulfur concentration is about 100 times greater than that experienced in the combustion chambers of jet engines. Microanalysis of these specimens indicated that the sulfidation, i.e., sulfur penetration of the brazing alloy was generally less than but never greater than such penetration of the base metal.

All of the alloys listed in Table 1 have been tested and utilized in a manner similar to that described above. Similar improvements and advantages were identified in the utilization of these alloys.

It is within the scope of the invention that the gold content of the alloy be in the range of 2570%, the palladium content from to 30%, the nickel content from to 40%, chromium from 4 to 12%, and .01 to 2% yttrium. The invention also contemplates the addition to these alloys of up to about 2% by weight of a refractory metal selected from the group consisting of tungsten, tantalum and molybdenum. The preferred compositions among those described in Tablel are Alloy Nos. 1, 2 and 3 with the yttrium content in each of 0.1% to 0.5

What is claimed is:

1. An alloy for brazing consisting essentially of 29 to 67% gold, 7 to 28% palladium, 19' to 38% nickel, 5 to 10% chromium, .01 to 2% yttrium, and up to 2% of the metal selected from the group consisting tungsten, tantalum and molybdenum.

2. An alloy for brazing consisting essentially of 29 to 67% gold, 7 to 28% palladium, 19 to 38% nickel, 5 to 10% chromium, and 0.1 to 2% yttrium.

3. An alloy for brazing consisting essentially of 29 to 30% gold, 25 to 27% palladium, 37 to 38% nickel, 6 to 8% chromium, and .01 to 2% yttrium.

4. An alloy for brazing consisting essentially of 45 to 47% gold, 22 to 24% palladium, 22 to 24% nickel, 6 to 7% chromium, and .01 to 2% yttrium.

5. An alloy for brazing consisting essentially of to 67% gold, 7 to 8% palladium, 19 to 22% nickel, 5 to 7% chromium, and .01 to 2% yttrium.

6. An alloy for brazing consisting essentially of 41 to 43% gold, 17 to 19% palladium, 3 1 to 33% nickel, 6 to 7% chromium, .01 to 2% yttrium, and about 1% molybdenum.

7. An alloy for brazing consisting essentially of 32 to 34% gold, 26 to 28% palladium, 28 to 30% nickel, 8 to 10% chromium, .01 to 2% yttrium, and about 1% tantalum.

8. An alloy for brazing consisting essentially of 29 to 30% gold, 25 to 27% palladium, 37 to 38% nickel, 6 to 8% chromium and 0.1 to 0.5% yttrium.

9. An alloy for brazing consisting essentially of 45 to 47% gold, 22 to 24% palladium, 22 to 24% nickel, 6 to 7% chromium, and 0.1 to 0.5 yttrium.

10. An alloy for brazing consisting essentially of 65 to 67% gold, 7 to 8% palladium, 19 to 22% nickel, 5 to 7% chromium, and 0.1 to 0.5% yttrium.

11. An alloy for brazing consisting essentially of 25 to 70% gold, 5 to 30% palladium, 15 to 40% nickel, 4 to 12% chromium, and .01 to 2% yttrium.

References Cited UNITED STATES PATENTS 3,148,053 9/1964 Spaletta --134 L. DEWAYNE RUTLEDGE, Primary Examiner E. L. WEIS-E, Assistant Examiner U.S. Cl. X.R. 75165, 172

P0405) UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 577 233 Dated y 4 r 71 Nicholas T. Gamer It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the specification, column 2, line 41, delete "0.1%" and substitute therefor -.0l%--.

Column 4, claim 2, last line, delete "0.1%"and substitute therefor .01%-.

Signed and sealed this 3rd day of August 1971.

(SEAL) Attest:

EDWARD M. FLETCHER,JR. WILLIAM E. SGHUYLER, JR. Attesting Officer Commissioner of Patents 

